Path: utzoo!attcan!uunet!paralogics!shaw
From: shaw@paralogics.UUCP (Guy Shaw)
Newsgroups: comp.lang.postscript
Subject: Re: Optical Illusion
Summary: M. C. Escher style impossible triangle
Message-ID: <266@paralogics.UUCP>
Date: 13 Apr 90 06:03:50 GMT
References: <1034@cnca.cnca-cam.fr> <1144@chinacat.Unicom.COM>
Organization: Paralogics; Santa Monica, CA
Lines: 65

In article <1144@chinacat.Unicom.COM>, woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) writes:

> . . . How about y'all posting some.  Does anyone have any Escher? (sic)

I don't have an impossible nut, but here is an impossible triangle.

%!
% M. C. Escher style impossible triangle
% written by Guy Shaw

% Things that are easy to play with:
% Position on paper, overall size, and linewidth
/inch { 72 mul } bind def

2 inch dup translate
3 inch dup scale
1 3 inch div setlinewidth

% Thickness parameter:
% /Thick is the thickness of the structural members of the triange,
% as a fraction of the height of the triangle.
% Reasonable looking impossible triangles can be obtained with Thick <= 1/6.
% right at /Thick == 1/6, there is no space left inside the triangle.
% /Thick > 1/6 yields bizarre, but not very interesting results.
% /Thick < 1/20 is less interesting, because the "impossibility"
% is not so striking when the structural members are that thin.
% A good "standard" value is 1/8.

/Thick 1 8 div def

% You would not normally want to change anything that follows.

/Tall 1 def
/HalfThick Thick .5 mul def

newpath
	HalfThick Thick moveto
	Thick  0 lineto
	1 Thick sub  0 lineto
	1 HalfThick sub  Thick lineto
	.5 HalfThick add  Tall Thick sub lineto

	1 Thick sub  0 moveto
	.5 HalfThick add  Tall 3 Thick mul sub lineto
	Thick 3 mul  Thick 2 mul lineto

	1 Thick 2.5 mul sub  Thick moveto
	.5  Tall Thick 4 mul sub lineto
stroke

newpath
	HalfThick Thick moveto
	1 Thick 2.5 mul sub  Thick lineto
	HalfThick neg  Thick rlineto
	Thick Thick add  Thick Thick add lineto
	.5 HalfThick add  Tall Thick sub lineto
	Thick neg  0 rlineto
	closepath
fill

showpage
-- 
Guy Shaw
Paralogics
paralogics!shaw@uunet.uu.net  or  uunet!paralogics!shaw